This relates generally to electronic devices, and more particularly, to electronic devices with displays.
Electronic devices often include displays. For example, cellular telephones and portable computers often include displays for presenting information to a user.
Liquid crystal displays contain a layer of liquid crystal material. Display pixels in a liquid crystal display contain thin-film transistors and electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a display pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the display pixel.
In a conventional liquid crystal display, the display pixel thin-film transistors are formed on a glass substrate. For example, gate and source-drain structures for each display pixel thin-film transistor can be formed over the glass substrate. The gate structure of each display pixel thin-film transistor is coupled to a gate line that carries signals to selectively turn on the thin-film transistors, whereas one of the source-drain structures of each display pixel thin-film transistor is coupled to a data line that carries image/video signals to be written into each display pixel.
A silicon nitride passivation layer is then formed on the thin-film transistors. A layer of silicon oxide is formed on the silicon nitride layer. Data line metal routing structures are often formed on the layer of silicon oxide. An acrylic organic planarization layer is then formed on the silicon oxide. The silicon oxide layer and the acrylic organic planarization layer generally exhibit different indices of refraction.
During operation of the liquid crystal display, backlight is used to illuminate the display pixels. Due to the difference in the refractive index of the silicon oxide layer and the refractive index of the acrylic organic planarization layer, a substantial portion of the backlight may be reflected back into the display, which reduces the transmittance and efficiency of the liquid crystal display. Moreover, the silicon oxide layer needs to be relatively thin to reduce silicon oxide film stress, which can cause breakage of the glass substrate. As a result, it is also challenging to reduce any parasitic capacitance that exists between the thin-film transistor gate structures and the data line metal routing structures. Data line capacitive loading can significantly degrade the display performance and consume excessive power.
It would therefore be desirable to be able to provide electronic displays with improved transmittance and reduced data line loading.